1. Technical Field
This invention relates to a infrared (IR) flare dispensing towed decoy, and more particularly, to such an IR flare dispensing towed decoy that is electronically configurable to vary its IR emissions and burn duration.
2. Background Art
Infrared-guided and radar-guided missiles pose the primary threats to military aircraft engaged in a combat environment. These missiles use their radar and IR guidance to home in on aircraft, thereby substantially increasing their probability of a "hit".
One method of defeating radar-guided missile attacks is to tow a decoy behind the host aircraft that is a more attractive radar target than the aircraft itself, so that the attacking missile chooses the towed decoy as opposed to the aircraft. The assignee hereto has pioneered this particular technology, developing a system for countering radar-guided weapons which is currently entering production for Air Force and Navy combat aircraft under the nomenclature of AN/ALE-50. However, to date no similar capability for defeating non-imaging IR-guided missiles has been developed.
Current military aircraft are particularly vulnerable to attack from IR-guided surface-to-air and air-to-air missiles. Statistics gathered from analysis of aircraft losses in hostile actions since 1980 show that almost 90% of these losses have been the result of IR-guided missile attacks. Thus, IR-guided missiles have become a formidable threat to military aircraft. These missiles can either be guided to their target entirely using IR-guidance or can initially utilize radar guidance and then switch over to IR guidance as they come into closer proximity to the target. In regards to the latter approach, IR-guided missiles can be cued via radar, or a passive Infrared Search and Track (IRST) system employed with the missiles can be alerted and properly oriented via a data link from a ground based surveillance or early warning radar. Optimally, however, IR-guided missiles are launched at an aircraft without the use of radar cueing, which often alerts an aircrew to an impending missile attack when the radar signals are detected by an on-board radar warning receiver. These IR-guidance only missiles are essentially passive and can be launched as a result of visual observation of the approaching aircraft, via self cueing or with assistance from a IRST system. In the absence of warning to the target aircraft, these missiles have a high degree of lethality.
The number and variety of infrared guided missiles pose a significant challenge to the development of an effective countermeasure in that the missiles tend to employ a wide variety of IR counter-countermeasure (IRCCM) capabilities. This makes it difficult to devise techniques that will be effective across the spectrum of IR guided missile threats and insensitive to the presence/absence or type of IRCCM being employed.
A number of methods have been used in an attempt to reduce the lethality of IR-guided missiles. Aggressive maneuvering of the target aircraft is often attempted if there is sufficient warning of an approaching missile. Also, pyrotechnic or pyrophoric flares that are forcibly ejected from on-board magazines using pyrotechnic squibs as the motive source have been employed. However, these devices burn at the necessary intensity for only a short period of time. In addition, gravity quickly separates the flares from the dispensing aircraft removing them from the missile seeker's field of view--thus limiting or reducing their effectiveness. These IR flares can also be identified by some missiles and rejected because they tend to initially provide more intense IR emissions than the aircraft. Furthermore, some missiles can also identify IR emitting flares by their IR spectrum.
Another current countermeasure involves the use of an IR jammer. Infrared jammers attempt to confuse missile seekers by "blinking" IR energy at an approaching missile. This energy is modulated at rates designed to confuse the signal processing circuitry of the attacking missile and induce sufficient angle error in its guidance mechanism so as to cause a miss. However, IR jammers have not been particularly successful for a number of reasons. The lamp sources of IR energy have difficulty generating sufficient intensity to overcome the aircraft engine's IR signature. They normally are required to be omni-directional since the direction of missile attack is not generally known. This further dilutes their energy density. If they are focused into a controlled beam to increase their energy on the IR missile seeker, they require fairly accurate pointing information which is not currently available on fighter aircraft. Finally, since different types of IR-guided missiles rarely use the same signal processing technology, it has not been possible to create a generic jamming modulation effective against all missiles. This can only be accomplished if the jammer designer has intimate knowledge of the missile seeker which allows him/her to exploit its design vulnerabilities. Clearly, this requires knowledge gained via exploitation of captured or covertly obtained missiles or through other intelligence sources. However, this is an impractical approach given the number and variety of IR-guided missile types.
In conclusion, the aforementioned approaches have proven to be individually and collectively inadequate to assure the survivability of military aircraft threatened by IR guided missiles. Therefore, what is needed is a system for distracting IR missiles from a target aircraft that tracks with the movement of the aircraft and provides the same IR spectral characteristics as the aircraft to be protected. Furthermore, this system should be able to control its radiant intensity so as to attract IR-guided missiles which are able to more closely discriminate between aircraft IR signatures and IR decoy launched flares. Additionally, the system should exhibit a sufficient burn duration to provide protection over a reasonable length of time against a possible missile attack.